1. Industrial Use Field
This invention pertains to molded parts used for photographic sensitive materials and resin compositions used to make such parts as magazines which house photographic sensitive materials like photo-film and printing paper or springs and rollers that are used around the photographic sensitive materials.
2. Existing Technology
Polyacetal resin which is a thermoplastic resin is used as a molding composition for machine bearings, gear wheels, rollers, cams, clips and plate springs because of its excellent mechanical properties, heat resistance, friction resistant and anti-abrasion properties and fatigue resistance property. However, a small amount of the monomer formaldehyde is dissolved in molded parts made of the polyacetal resin and its slow release into the air causes deterioration of work environment and compromized work efficiency and, in some cases, may lead to harmful result to the end use objective. For example, because chemically active formaldehyde is present, the polyacetal resin causes some concern to be used as food and medical packaging material.
Also, it is known that formaldehyde has detrimental effect on photographic sensitive materials such as photographic film and printing paper. While a silver halide emulsion is used in these photographic sensitive materials, formaldehyde has the ability to reduce silver halides, resulting in chemical fogging. Therefore, polyacetal resins, in general, cannot be used as a resin composition of magazines that receive photographic sensitive materials and various molded parts that are used around them. Consequently, metals are often used to make parts that require sufficient elasticity such as a film pressing board.
Considering these situations and in order to reduce concentrations of formaldehyde gas in the molded parts made of acetal resin, Japanese Kokai 1992-34548 describes hydrazide compounds to be used as an additive, and Japanese Kokai 1994-107900 describes the use of fatty acid ester of polyvalent alcohol compound as an additive.
Problems that Invention Attempts to Solve
But, when a hydrazide compound is added as an additive to polyacetal resin, there is a certain danger of its byproduct, hydrazine itself, functioning as a reducing agent of photographic sensitive materials. Also, when a fatty acid ester of polyvalent alcohol compound is used as an additive, its effect to suppress formaldehyde is not sufficiently and practical problems persist for its use as a resin composition to make molded parts for photographic sensitive materials.